There was no indication in the discussions between the pilots and the air traffic controllers that there were problems with the aircraft.
Hersman earlier said investigators are looking into what role the shutdown of a key navigational aid may have played in the crash. She said the glide slope — a ground-based aid that helps pilots stay on course while landing — had been shut down since June.
She said pilots were sent a notice warning that the glide slope wasn’t available. Hersman told CBS’ “Face the Nation” that there were many other navigation tools available to help pilots land. She says investigators will be “taking a look at it all.”
Since the crash, clues have emerged in witness accounts of the planes approach and video of the wreckage, leading one aviation expert to say the aircraft may have approached the runway too low and something may have caught the runway lip — part of a seawall at the foot of the runway.
San Francisco is one of several airports around the country that border bodies of water that have walls at the end of their runways to prevent planes that overrun a runway from ending up in the water.
Since the plane was about to land, its landing gear would have already been down, said Mike Barr, a former military pilot and accident investigator who teaches aviation safety at the University of Southern California.
It’s possible the landing gear or the tail of the plane hit the seawall, he said. If that happened, it would effectively slam the plane into the runway.
Noting that some witnesses reported hearing the plane’s engines rev up just before the crash, Barr said that would be consistent with a pilot who realized at the last minute that the plane was too low and was increasing power to the engines to try to increase altitude.